1. Field of the Invention
The present invention relates to a heater which can be used to heat a lubricating fluid such as an engine oil or a transmission fluid.
2. Description of Related Art
Some machines operate, while rubbing parts against each other. For example, in an internal combustion engine such as an internal engine, a large number of parts rub against one another in a process of the up-and-down movement of a piston in a cylinder. When the parts rub against one another in this manner, wear or heat generation occurs on the parts, and defects are generated in the machines. Therefore, a lubricating fluid is used to decrease friction when the parts rub against one another, thereby suppressing the wear and the heat generation. For example, an engine oil is used as the lubricating fluid to suppress the wear and the heat generation on the parts in the engine. The lubricating fluid is indispensable in suitably operating the machine in this manner. However, when the lubricating fluid is in a low-temperature state, a viscosity of the lubricating fluid becomes high. In consequence, a problem occurs that friction cannot sufficiently be lowered. There occurs another problem that the lubricating fluid cannot be supplied to a targeted portion, or the like. To cope with this problem, the lubricating fluid is heated by using a heater to raise the temperature of the lubricating fluid, thereby appropriately lowering the viscosity thereof. When the heater is used in this manner, it is possible to lower the viscosity of the lubricating fluid. On the other hand, a disadvantage occurs that when the lubricating fluid is excessively heated by the heater, the deterioration of the lubricating fluid is caused. Consequently, there has been disclosed a heater including a mechanism which does not excessively heat the lubricating fluid (e.g., Patent Documents 1 to 3).    [Patent Document 1] JP-A-2003-74789    [Patent Document 2] JP-A-63-16114    [Patent Document 3] JU-A-63-12607